Heater tube for furnaces



Nov. 5, 1940. A. RUCKSTAHL HEATER TUBE FOR FURNACES Filed Oct. 10, 1938 Amway Patented Nov. .5, 1940 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to heater tubes, commonly termed radiant tubes, for furnaces of various types, for instance and not by way of limitation, furnaces for the heat treating or processing of metals or for various other purposes as, for instance, enameling metals at various tempera- ,tures and in the presence of a desired gaseous atmosphere provided either for the protection or the processing of materials under treatment.

The principal purpose of the invention is to provide a new and improved heat radiating tube of a simple design and easily removable from the furnace for repair even while the furnace is under heat and of such construction as to maintain the temperature of the tube practically uniform throughout the length thereof within the furnace.

It has heretofore been known to heat a furnace by a heated tube or tubes but it is not possible to control the temperature of the tube at various points of its length, it being hotter at the intake than at the discharge end and no way has heretofore been provided to enable an operator to vary the temperature of the tube in portions of its length,

This invention seeks to provide a new construction of heater tubes for furnaces, particularly a tube formed with two passageways so constructed that the gases in combustion pass from an outer end of the tube into the furnace in one direction and back in a passageway parallel thereto to an exhaust line outside the furnace, apertures being provided between the two passageways of comparatively small cross sectional area in respect to the cross sectional area of either passageway and through which the heated gases may pass from the inflowing to the outfiowing portion of the stream at various points to thereby maintain the tube uniformly or variably heated as may be required for specific purposes.

It is further a feature and object of the invention to provide a gas fired heater tube for furnaces of various types having a gas burner with which air and gases are mixed to discharge in conjunction in the tube and to vary the position of the discharge end of the firing tube longitudinally of the passageway to thereby effect the distribution of the heated gases and by such adjustnumber of my improved tubes and their relationship thereto.

Fig. 2.is a cross section taken on line 22 of Fig. 1.

Fig, 3 is an enlarged sectional view of my improved heater tube.

Fig. 4 is a partial longitudinal section taken on line 4-4 of Fig. 3 showing the character of dividing wall provided in the tube.

Fig. 5 is a cross section of a tube in its preferred form taken on line 55 of Fig. 4.

In Figs. 1 and 2, I have shown the general location of the heater tubes, there being a number of such tubes l, I in the upper part of the furnace and 2, 2 in the lower part of the furnace through which material is moved on a. trackway 3, the material being indicated at 4 in Fig. 2 as being carried by a tray 5 which is slidable on the trackway.

The furnace here shown is of the well known pusher type carburizing furnace and is given only by way of illustration to show a use of the heater tube and not by way of limitation as the heater tube may be used in various types of furnaces.

The preferred tube structure is shown more clearly in Figs. 3, 4 and 5 and comprises a tubular member 6 which is preferably of metal mounted in an aperture in the front wall 7 of the II and 22 and between the flange 22 and face of the furnace to thereby prevent any possibility of leakage of gases from the furnace or tube.

The tube shown is divided longitudinally by a horizontal wall, preferably formed of fire brick or other refractory blocks II which are formed, as by shaping the corners of a number of blocks at an angle to the side and end walls as indicated at H, to provide apertures permitting flow of gases in desired volume from the inlet passageway l3 to the upper outlet l4 of the tube. While the invention is not confined to the use of fire brick as a dividing wall, such character of wall structure is desirable as the combustion is more complete than is the case with a metallic separating wall.

The blocks H are supported on ribs .l5 provided on opposite sidewalls of the tube as indicated in Figs. 4 and 5 and the apertures formed between the blocks by reason of the hexagonal form of the opposite ends of the block extend beyond the inner face of the flanges I5 thus providing for a flow of gases from the lower passageway I! to the upper passageway ll which is preferably somewhat less in cross sectional area than the cross sectional area of the passageway IS. The blocks Ii may also be of less width than the distance between opposite side walls of the tube and may be moved on the said ribs tovarythe size of the apertures between any desired number of the blocks. This also provides for flow of gas from the inlet to the outlet passageway.

I have indicated diagrammatically a burner tube IS in Fig. 3 which is to be understood as being of the ordinary well known form to which gas is supplied by the tube I! and discharging at a nozzle I8 in the outer end of the passageway l3, it also being understood that air is introduced with the gaseous mixture as by the tube ll depending upon the character of burner utilized, it being possible to provide the desired combustion of gas for discharge through the conduit I! to the burner without necessity of air. The burner illustrated is of the well known low pressure type. The burned gases discharge exteriorly of the furnace by a. conduit I9 opening through the head 20 carrying the burner and attached to the tube 6 by a flange 2| secured to flanges 22 of the tube. The tube [9 discharges toan exhaust conduit l9. Thus, provision is made for a flow of gases into the lower passageway l3 and these gases pass principally to the end 23 of the tube and thence to the upper parallel passageway H.

In this character of heater tube as previously constructed, the gases as they reach the inner end 23 of the tube have dropped in temperature and the gases passing through the passageway ll are constantly dropping in temperature and thus the tube would be unevenly heated. To avoid such undesirable condition, I have provided apertures between some of the blocks Ii whereby some of 40 the highly heated gases discharge from the passageway l3 into the passageway H which thus is filled with heated gases approximating the temperature of the gases in the passageway II. This, of course, may be accomplished by spacing 45 the blocks and it is thus to be understood that the form of the block described is only one of the forms which may be utilized in the formation of the dividing wall.

With such an arrangement of dividing wall 60 having apertures or passageways formed therein to provide for a flow of gas from the section ii to the section H, the apertures may be varied in size so that moregas will pass from a section i3 to a section I4 at some points than at others and 55 I have also found in practice that the burner tube I6 is preferably to be slidably mounted in the portion of the head 20 as shown in order that the point of discharge of hot gases into the section l3 may be variedthat is, the point of dis- 60 charge may be to the rear or forward of the position shown and thus to vary the intensity of the heat at certain points. By positioning the end of the burner nozzle IS a greater distance intothe heater tube 6, the gases passing through the up- 65 per passageway of the tube will discharge at higher temperature than would be the case with the nozzle IS in the position as shown. Likewise movement of the nozzle I 8 to the left of the position shown results in a lowered temperature 70 of gases discharging from the upper passageway.

Thus if the tube is unevenly heated in any one position of the burner, the: burner may be shifted to increase or decrease the temperature at points as may be required to overcome the objectionable 75 condition. A further means of preventing such hot or cold spots is provided by the arrangement of the blocks Ii separating the tube into an upper and a lower passageway. The hexagonal form of the blocks may be varied to provide larger or smaller apertures therebetween or by 5 1 making the blocks of less width than the width of the tube. In either case a greater or less volume of gases may pass from the lower to the upper passageway at various points of its length. Obviously the gases flowing through the lower passageway would, if there be an imperforate dividing wall therebetween, be of higher temperature than in the upper passageway but, by the disposition of the movable blocks to increase or to decrease the area or number of apertures at any point longitudinally of the tube 6, a greater or less volume of flow of gases per unit of time is permitted through the dividing wall at any point or points of too great or too little heat in the upper passageway. By such arrangement inequality of heating may be prevented.

The tubes are usually grouped in some desired manner and, for instance, the tubes I could be separately connected with the supply of gas while the tubes 2 in any one of the spaces 2' in the lower part of the furnace may be separately connected with a gas supply and thus the supply of fuel may be varied to tubes in various sections of the furnace, this depending principally upon the material to be treated requiring more heat at some points than at others or for other reasons and all within the control of an operator through variation of the series of tubes in operation to control the temperature of the' furnace chamberthat is, to be more greatly heated at some points than at others or gradually heated as it is passed through the furnace, etc., depending upon the requirements of the material being submitted to the heat treatment.

One of the features of the invention resides in the structural arrangement providing for ready removability of the tube from the furnace, the structure illustrated being of a character to permit the removal of the tube while the furnace is under continuing heat. Heretofore, it has been usually necessary to shut off the fuel supply and allow the furnace to cool before a defective tube may be removed. In my construction, as here tofore stated, the forward end of the burner is held in place by clamp'elements and the inner end has a tube! riding on a roller l0.

In alignment with the tube '9, which is secured to the end of the burner tube 6 and not open thereto, I provide an aperture 35 in the furnace wall 36 as shown in Fig. 3 which is preferably closed by a plug element 31. By removal of this plug, a long rod (not here shown) may be introduced through the'aperture 35 andinto the end of the tube 9. Upon release of the clamping elements 30 and 3| which support the inlet end of the tube at the front furnace wall 38 and disconnection of the heads with the air and gas inlet and exhaust pipes, the tube may be moved longitudinally through the furnace wall 38 while the inner end of the tube remains supported by the rod introduced into the member 9. It will be evident by this arrangement that, while the furnace is under heat, the heater tube may be removed and a new heater tube introduced in place by introducing the element 9 onto the rod atthe 70.

front side of the furnace and then move the tube and the rod to the left of Fig. 3 to bring the element 9 to rest on the roller III. This arrangement provides for a ready and inexpensive repair of the furnace without a material cessation of operation of the furnace thus avoiding the expensive delay encountered in the present arrangement of furnaces of this general type.

Broadly, the invention involves a tubular structure formed to provide parallel passageways which are united at the inner end of the tube to provide for continuous flow from an inlet to an outlet conduit at the opposite end of the tube and so constructed as to provide a predetermined number of passageways for a flow of gases in predetermined volume from the inlet to the outlet passageway as hereinbefore described whereby the tube may be maintained under practically uniform temperature in that portion thereof within the furnace or may be varied in temperature particularly by reason of transfer of portions of gases in the intake passageway to the outlet passageway and thus by variation in form of apertures or passageways provided in the dividing wall, any desired result for specific purposes may be attained.

Having thus fully described my invention, its utility and mode of operation, what I claim and desire to secure by Letters Patent of the United States isl. A heater tube for use in furnaces adapted for the processing of material through influence of heat and having an opening in the wall thereof to receive the tube, comprising a horizontal positioned tube having parallel upper and lower passageways in the portion thereof to be positioned within the furnace, said passageways being united at the inner ends providing for continuous flow of gases in combustion into the tube through the lower passageway and out of the tube through the upper passageway. a burner for discharging the gases in combustion into the outer end of the lower passageway. and means whereby a limited volume of gases may pass from the infiowing portion of the stream to the outfiowing portion of the stream at several points spaced longitudinally of the passageways.

2. A heater tube for the purpose described comprising a tubular element, a dividing wall therewithin extending from one end to adjacent the opposite end and separating the tube into parallel upper and lower passageways in full communication at one end and a separate inlet and outlet at the opposite end, a gas injecting and firing means at the inlet end of the lower passageway, the gases in combustion passing to the opposite end of the tube and to the upper passageway parallel therewith, the said dividing wall having a series of apertures therein spaced longitudinally of the tube providing for discharge of gases in combustion from the inlet passageway to the outlet passageway to maintain the temperature of the walls of the tube forming the outlet passageway at a temperature approximating that of the inlet passageway.

3. A heater tube for the purpose described comprising a tubular element, a dividing wall therewithin extending from one end to adjacent the opposite end and separating the tube into parallel upper and lower passageways in full communication at one end and a separate inlet and outlet at the opposite end, a gas injecting and firing means at the inlet end of the lower passageway, the gases in combustion passing to the opposite end of the tube and t0 t e upp r passageway parallel therewith, the said dividing wall having a series of apertures therein spaced longitudinally of the tube providing for discharge of gases in combustion from the lower inlet passageway to the upper outlet passageway to maintain the temperature of the walls of the tube forming the upper outlet passageway at a temperature approximating that of the lower inlet passageway, and means for varying the point of injection of the gases in combustion into the tube in respect to the said apertures.

4. A heater tube for furnaces comprising a tubular member formed at the outer end to provide an inlet and an outlet for gases in combustion, a dividing wall in the tube separating the inlet from the outlet and providing two parallel passageways in communication at the inner ends through which the gases flow in opposite directions, said wall comprising a series of fire resistant blocks of such shape and so arranged as to provide openings between the passageways,supporting means within the tube for sustaining the blocks in position, the combined cross sectional area of said openings being less than the cross sectional area of the inlet passageway and providing for discharge of gases in combustion from the inflowi-ng to the outfiowing stream to thereby prevent too rapid a drop in temperature of the outfiowing gas stream and maintaining the tube comparatively uniformly heated.

5. A heater tube for furnaces comprising av tubular member formed at one end to provide for an inlet for gases in combustion and an outlet, a dividing wall extending from the said inlet and outlet end and extending to near the opposite end and providing two parallel passageways in full communication at the inner ends through which the gases flow in continuity from the inlet to the outlet, said dividing wall comprising a series of fire resistant blocks, a rib on opposed inner faces of the tube for slidably supporting the blocks in a horizontal plane, some of the said blocks being shaped to provide apertures between the inlet and outlet, the slidability of the blocks providing for adjustment of the spaces therebetwen permitting a flow of gases from the inlet to the outlet passageway of the tube whereby the outflowing stream is maintained at a desired temperature in respect to the temperature of the inflowing stream for a greater portion of the length'of the tube.

6. A heater tube for furnaces comprising a tubular member formed at one end to provide an inlet for gases in combustion and an outlet therefor, a dividing wall extending from betweenthe inlet and outlet to near the opposite end and providing two parallel passageways through which the gases flow in continuity, means for injecting gases in combustion into the inlet end of the inlet passageway, said dividing wall being of a fire resistant character and provided with apertures permitting a flow of gases from the inlet passageway to the outlet passageway of the tube, said injection means for gases being adjustable longitudinally of the inlet passageway to vary the position thereof in respect to the said apertures in the dividing wall whereby the temperature of the outfiowing stream in the outlet passageway may be varied.

ALFRED RUCKSTAHL. 

